Re: [Qemu-devel] [PATCHv3 3/6] block: add a knob to disable multiwrite_merge

[Eric Blake <eblake@redhat.com>]

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On 10/25/2014 10:55 AM, Peter Lieven wrote:
> The block layer silently merges write requests since
> commit 40b4f539. This patch adds a knob to disable
> this feature as there has been some discussion lately
> if multiwrite is a good idea at all and as it falsifies
> benchmarks.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---

> +# @write-merging: #optional enable the merging of write requests
> +#                 also known as multiwrite_merge (Since 2.2)
> +#                 (default: true, but this might change in the future
> +#                 depending on format/protocol/features used)
>  #
>  # Since: 1.7
>  ##
> @@ -1198,7 +1205,8 @@
>              '*rerror': 'BlockdevOnError',
>              '*werror': 'BlockdevOnError',
>              '*read-only': 'bool',
> -            '*detect-zeroes': 'BlockdevDetectZeroesOptions' } }
> +            '*detect-zeroes': 'BlockdevDetectZeroesOptions',
> +            '*write-merging': 'bool' } }

This says it is boolean...


> +++ b/qmp-commands.hx
> @@ -2104,6 +2104,7 @@ Each json-object contain the following:
>           - "iops_size": I/O size when limiting by iops (json-int)
>           - "detect_zeroes": detect and optimize zero writing (json-string)
>               - Possible values: "off", "on", "unmap"
> +         - "write_merging": enable merging of write requests (json-bool)
>           - "image": the detail of the image, it is a json-object containing
>              the following:
>               - "filename": image file name (json-string)
> @@ -2181,6 +2182,7 @@ Example:
>                 "iops_wr_max": 0,
>                 "iops_size": 0,
>                 "detect_zeroes": "on",
> +               "write_merging": "true",

...but this is not a JSON bool.  s/"true"/true/

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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